been saying a lot of things about his proposals that just aren't true-- like that he's going to raise taxes on the middle-class. he says that will end at tonight's debate. his aides say he'll try to prosecute the case on the economy against the president, scott, saying point blank "this economy cannot afford four more years of president obama." >> pelley: thanks, jan, also covering the debate is our cbs news political director john dickerson. john, what are the pitfalls that are facing the candidates possibly? >> for governor romney, he's got two jobs: one is to say why the president has failed and the second is to sell himself. to do that job, he has to be aggressive, kind of in the president's face. for the second job he has to offer something people find attractive so the challenge for him is getting the mix right. the challenge for the president is staying on script, talking about how he has been working for the middle-class and not getting knocked off by governor romney who he doesn't have a great deal of personal regard for. so he has to not look defensive. >> pelley: john, thank you